1. Field of the Invention
This invention relates to an optical measuring device, and more particularly to improvements in an optical measuring device, wherein parallel scanning ray beams are utilized to measure dimensions of a workpiece being measured.
2. Description of the Prior Art
Heretofore, there has been adopted an optical measuring device wherein rotary scanning ray beams are converted by a collimator lens into parallel scanning ray beams being passed through this collimator lens and a condensing lens, a workpiece being measured is interposed between the collimator lens and the condensing lens, and dimensions of the workpiece being measured are measured from the time length of a dark portion or a bright portion generated due to the obstruction of the parallel scanning ray beams by the workpiece being measured.
More specifically, as shown in FIG. 1, laser beams are oscillated from a laser tube 1 toward a stationary mirror 2, the laser beams thus reflected are converted into scanning beams by a rotary mirror 3, the scanning beams are converted beams by a rotary mirror 3 having two surfaces, the scanning beams are converted into parallel scanning ray beams by a collimator lens 4, an article 6 being measured interposed between the collimator lens 4 and a condensing lens 5 is scanned at high speed by the parallel scanning ray beams, and dimensions of the workpiece 6 being measured are measured from the time length of a dark portion or a bright portion generated due to the obstruction of the parallel scanning ray beams by the workpiece 6 being measured.
The bright and dark portions of the parallel scanning ray beams are detected as variations in output voltage of a light receiving element 7 disposed at the focal point of the condensing lens 5. Signals from the light receiving element 7 is fed to a pre-amplifier 8, where they are amplicied (Refer to v), and then, fed to a segment selector circuit 9. This segment selector circuit 9 is adapted to generate a voltage V to open a gate circuit 10 only for a time t, during which the article 6 being measured is scanned, from the time of the voltage output of the light receiving element 7 and feeds the same to the gate circuit 10. A continuous clock pulse CP is fed to this gate circuit 10 from a clock pulse oscillator circuit 11, whereby the gate circuit 10 generates a clock pulses P for counting the time t corresponding to the outer diameter of the workpiece 6 being measured and feeds the same to a counter circuit 12. Upon counting the clock pulses P, the counter circuit 12 feeds a count signal to a digital indicator 13, where the outer diameter of the workpiece 6 being measured is digitally indicated.
In FIG. 1, designated at reference numeral 14 is a synchronous sine wave oscillator circuit, 15 a power amplifier and 16 a synchronous motor. The synchronous motor 16 rotates the rotary mirror 3 in synchronism with the clock pulses in response to synchronous signals fed from the synchronous sine wave oscillator circuit 14 in response to the continuous clock pulses CP fed from the clock pulse oscillator circuit 11, whereby the measuring accuracy is maintained.
The above-described measuring method has been widely utilized because the lengths, thickness and the like of moving workpieces and workpieces heated to a high temperature can be measured at high accuracies in non-contact relationship therewith.
However, in the case of the above-described device, since the rotary mirror 3 has two surfaces only, the angle of use .theta. for generating the scanning beams is small as shown in FIG. 1, thus presenting the disadvantage that the measuring speed is low. More specifically, if the rotary mirror rotates at a constant speed, then the number of measurements in a predetermined time period is small, and consequently, it takes a long time to conduct a predetermined number of measurements.
In contrast thereto, it might be thought of to try to use a rotary mirror having three or more surfaces, however, in that case, the prodiction thereof results in increased cost.
It might be thought of to try to increase the rotational speed of the rotary mirror, however, in this case, the resolving power, i.e., mm/pulse is determined by a scanning speed per unit length (specific scanning speed) of the workpiece being measured, the resolving power is in inversely proportional to this specific scanning speed, and hence, the increase in rotational speed results in decreased resolving power. On the other hand, it might be thought of to try to improve the averaged accuracy by the increase in the number of scannings, with the specific scanning speed being kept constant. In this case, however, turning with electric circuit including the oscillator becomes complicated and it is not preferable from the viewpoint of increasing the response speed to a high speed.